#include <stdio.h>
//練習問題G
int func(int n){
int a=1, b=2, c=1;
int i;
if (n == 1) return a;
if (n == 2) return b;
for (i = 3; i <= n; i++) {
c = -2 * b + 2 * a;
a = b;
b = c;
}
return c;
}
int main(void) {
int n = 3;
printf("数列anについて, n=%dのときの値は%d\n", n
, func
(n
)); return 0;
}
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